Cancer still accounts for a large percentage of death cause deriving from diseases and many molecular targeted medicines for cancer treatment are developed. The effect of the use of such anti-cancer agent used in the treatment may be increased by measuring the blood concentration of anti-cancer agent at diagnosis. As such, knowing the blood retention state of a drug is the most important objective in the interdisciplinary studies including medicine and biology.
Proteins have a specific conformational structure and the structure renders the specificity. In particular, the conformational structure of the Fab part of the antibody protein is an essential structure of the detection of a specific antigen in the biological body and plays a role in the antibody reaction. In the recent years, the development of molecular targeted medicines with the focus on the specific recognition ability of these antibody proteins have progressed rapidly and has dramatically improved the 5 years survival rate in cancer patients. For example, bevacizumab which is one of the antibody molecular targeted medicines that is sold under the product name of Avastin has a feature of reducing the proliferation speed of cancer by inhibiting angiogenesis. Because cancer cells actively perform cell proliferation as compared to normal cells in general, they require more nutrients and oxygen than normal cells, and thus, form blood vessels around the cancer tissues. As for angiogenesis, vascular endothelial cell growth factor (VEGF) is required and bevacizumab has an effect to inhibit this vascular endothelial cell growth factor. As such, bevacizumab inhibits angiogenesis around the cancer cells, and by blocking the nutrients provided to the cancer cells, it inhibits the proliferation of cancer cells. Accordingly, bevacizumab has no toxicity on cancer cells, has an advantage that it could be combinedly used with other anti-cancer agents, and thus, it is widely used as cancer therapeutic drugs. Therefore, bevacizumab is used for the treatment of colon cancer, rectal cancer, non-small-cell lung cancer, ovarian cancer, and breast cancer (for example, Non-Patent Documents 1 and 2).
For the measurement of blood bevacizumab concentration in the treatment, immune antibody method is used; however, this method has a drawback in that the operation is very complicated as well as that the test kit is expensive, and thus, it cannot be carried out frequently.
Because a single-stranded nucleic acid takes various conformational structures depending on its base sequence, a base structure having an affinity to a specific antigen can be found. Nucleic acids specifically adsorbing to these targets of purpose are called aptamers. For the screening of a novel aptamer, in vitro selection method is used as the most effective means. In particular, Systematic Evolution of Ligands by Exponential enrichment (SELEX) method is roughly divided into two steps: the selection of target nucleic acid molecules and the amplification of selected aptamers (for example, Patent Document 1). Repetition of the selection and amplification of the target nucleic acid molecule while increasing selectivity results in the obtainment of nucleic acid fragments with high affinity. Moreover, in the recent years, various improvements have been made, and reports are made on such as methods with superior efficiency and selectiveness which can collect aptamers with lesser number of cycles and methods obtaining aptamers binding not only to low molecules and proteins but also to cells and tissues (more precisely, to the molecules present on the surface) (Cell-SELEX method; for example, Non-Patent Document 3). In comparison to the conventional SELEX method, this method features the following: Analysis of proteins is unnecessary, various membrane protein aptamers present on the cell surface could be simultaneously selected, and furthermore, aptamers that further specifically bind to target cells could be selected. These aptamers have advantages that cannot be found in antibodies such as the following: synthesis can be performed chemically and in a short period of time, the modification of molecules can be performed economically, the action mechanism is simple, and hardly any immunogenicity is reported, which are additional advantages other than the high-affinity and specificity to a target that is featured by an antibody conventionally used in diagnosis and treatment.
Searching for a nucleic acid sequence having an affinity to an antibody protein, for example, other than to cells, can be easily carried out by using Protein A beads (Manufactured by Thermo Scientific Inc.) magnetic particles. When the aptamers having an affinity to the discovered antibody is used for diagnosis and examination, fluorescent dyes are introduced to the terminus, and detection under the fluorescence microscope is performed in most cases (for example, Non-Patent Document 2).
In medical oncology treatment, the combined use of anti-cancer agents can be effective. Here, two-agent combination therapy of those apart from molecular targeted medicines has demonstrated excellent results as compared to the conventional treatments; however, any combination showed equivalent results and the treatment results leveled off. On the other hand, antibody drugs such as molecular targeted medicines have presented a breakthrough achievement. The first report of molecular targeted medicine in Japan is IRESSA (Gefitinib). Although cases showing a dramatic therapeutic results using IRESSA (Gefitinib) are reported, no statistical effect has been shown. Nonetheless, it was believed to have a relative high effect in non-smokers and adenocarcinoma cancer patients. In 2009, Alimta was approved, and the combined used of this with cisplatin was shown to extend the survival rate of non-small-cell lung cancer except squamous cell carcinoma. Bevacizumab, which was approved subsequently, is referred to as an angiogenesis inhibitor, and by supplementing a vascular endothelial cell growth factor, angiogenesis is suppressed, the provision of nutrients to cancer cells is suppressed, and thereby cancer proliferation can be suppressed. Bevacizumab does not have toxicity on cancer cell itself, and thus, it is used in combination with other anti-cancer agents, e.g., the combined use with Carboplatin and Paclitaxel extended the overall survival period for 14.2 months.
As such, at present, antibody drug is a most commonly used molecular targeted medicine for cancer treatment. Moreover, antibody drugs suitable for the treatment of diseases such as Rheumatoid arthritis, Crohn's disease, and Asthma in addition to cancer are developed. Furthermore, these antibody drugs could cause problems such as side effects caused by excessive administration as in low molecular drugs and the measurement of blood concentration of antibody drug is difficult as compared to that of the low molecular drug. For this reason, at present, a simple measurement technique of blood concentration of a molecular targeted medicine is demanded to further improve the therapeutic effect.